1. Field of the Invention
The present invention relates to a code-multiplexing communication apparatus capable of removing an autocorrelated distortion with use of a simple circuit structure.
2. Description of the Related Art
There has proposed a code-multiplexing communication apparatus for realizing a large scale communication with transmission of multiplexing spread spectrum code.
In such code-multiplexing communicating apparatus, FIG. 7A shows a transmission unit of the communication apparatus, while FIG. 7B shows a reception unit thereof, noting that the number of code multiplex is 2 (or N=2) in this case.
Referring to FIG. 7A, the transmission unit has: a splitter 701 for splitting incoming transmitted data into two data signals; a spread code generator 702 for generating a spread code; spreaders 703 and 704 for carrying out a spreading for data signals split by the splitter 702; an adder 705 for adding signals from the spreaders 703 and 704; and modulator 706 for modulating signal from the adder 705 to output a transmitting signal.
Referring also to FIG. 7B, the reception unit has a de-spread code generator 711 for generating a spread code used for a de-spreading; a correlator 712 for carrying out a correlated calculation of an incoming received signal and the spread code; an equalizer 713 for equalizing an output signal from the correlator 712; and a coupler 714 for reproducing receiving data from an output signal of the equalizer 713.
With the constitution described above, the transmitted data is inputted to the splitter 701 that splits the data into two data signals. As a result, a half symbol rate of the transmitted data is inputted to each of the spreaders 703 and 704.
In addition, the spread code generator 702 generates a code used for the spreading in which such code is of the 11-bit Barker code, for example. The code supplied to the spreaders 703 and 704 also have a phase displacement corresponding to a displacement between two chips or two integrated circuits.
The spreaders 703 and 704 perform the spreading for the data signals split by the splitter 701 with use of the spread code supplied from the spread code generator 702. The adder 705 adds both the spread spectrum signals generated in the spreaders 703 and 704 to output a multiplexed signal.
The modulator 706 converts the multiplexed signal from the adder 705 into a radio wave to be able to transmit a transmitting signal as wireless.
In the case of reception unit as shown in FIG. 7B, the de-spreading code generator 711 generates a spread code used for a de-spreading and supplies it to the correlator 712.
The correlator 712 carries out a correlated calculation of an incoming received signal and the spread code from the de-spread code generator 711 to perform the de-spreading. A code-multiplexed signal is split into two signals that correspond to the two chips.
In the case of practical data transmission, a multi-path distortion is contained in the received signal on the transmission. Assuming that one of two codes to be multiplexed has a waveform caused by a multi-path distortion as shown in FIG. 8A (one pulse is expanded) and the other code to be multiplexed also has a waveform caused by the multi-path distortion as shown in FIG. 8B, for example, the waveforms of those codes being multiplexed interfere in each other, therefore, the waveform becomes a state as shown in FIG. 8C. Thus, the two codes may not be split under this state without arising error. To this end, the equalizer 713 removes such multi-path distortion and outputs a waveform as shown in FIG. 8D.
The equalizer 713 may be used a decision feedback equalizer shown in FIG. 9. In the case where a signal shown in FIG. 8A is supplied to the equalizer shown in FIG. 9, a decider 901 receives a first data xe2x80x9c1.0xe2x80x9d through an adder 903 to output data xe2x80x9c+1xe2x80x9d which is supplied to a delay element 902. Subsequently, data xe2x80x9c0.7xe2x80x9d is inputted to the adder 903, but the data xe2x80x9c0.7xe2x80x9d is inputted to the adder 903 from a multiplier 904 received data xe2x80x9c+1xe2x80x9d from the delay element 902, therefore, the output of adder 903 becomes xe2x80x9c0xe2x80x9d. Because of this, the decider 901 outputs xe2x80x9c0xe2x80x9d to the delay element 902. At the subsequent timing, data xe2x80x9c0.3xe2x80x9d is inputted to the adder 903. At this time, the output of adder 903 becomes xe2x80x9c0xe2x80x9d since data xe2x80x9cxe2x88x920.3xe2x80x9d is inputted to the adder 903 from a multiplier 906 which receives data xe2x80x9c+1xe2x80x9d from a delay element 905. That is, the output of multiplier 904 is xe2x80x9c0xe2x80x9d since the output of delay element 902 is xe2x80x9c0xe2x80x9d. As a result, the decider 901 outputs xe2x80x9c0xe2x80x9d. As described above, the equalizer 713 outputs a signal from which a multi-path distortion is removed. In the case where the multiplexed signal shown in FIG. 8C is inputted to the equalizer 713, the multi-path distortion is also removed, obtaining the output signal shown in FIG. 8D. It is noted that the coefficient of multiplication for the multipliers 904 and 906 may be determined by transmitting a preamble signal having predetermined information prior to the data transmission.
Accordingly, the signal being removed the multi-path distortion is supplied to the coupler 714 which converts the received signal into a signal form similar to the transmitted data to thereby output received data.
Japanese patent laid-open gazette 9-102758 discloses such code-multiplexing communication apparatus similar to that described above.
For the purpose of manufacturing more reliable apparatus, there would be some significant points, as follows. The code-multiplexing communication apparatus should be considered an autocorrelated distortion, that is, in the case of increasing the multi-path distortion, removal of the distortion may not be sufficiently carried out by the equalizer due to the affection of autocorrelated distortion.
For example, in the case of performing the correlated calculation with use of the 11-bit Barker code, an autocorrelated distortion represents a waveform as shown in FIG. 10A. That is, when coinciding the phase of waveforms, a value becomes xe2x80x9c+1xe2x80x9d, however, when displacing these phases, the value does not sufficiently become xe2x80x9c0xe2x80x9d, causing a distortion alternately indicated values xe2x80x9c0xe2x80x9d and xe2x80x9cxe2x88x921/11xe2x80x9d as distortion value. Assuming that a multi-path distortion is present in the transmission path as shown in FIG. 10B, not only an amplitude where the phase is matched changes, but also a distortion where the phase is displaced changes increasingly, with reference to the output of correlator 712 shown in FIG. 10C.
Under such condition of the large multi-path distortion, as the code multiplex is performed, the self-correlated distortion is accumulated, causing deterioration of the signal deciding performance.
It is possible to remove the autocorrelated distortion with use of the equalizer, however, in order of removing the distortion expanded to 21 chips, the constitution of equalizer becomes enormous size so that the tap coefficient of equalizer is required to make longer.
It is therefore an object of the present invention to provide a code-multiplexing communication apparatus capable of removing an autocorrelated distortion with use of a simple circuit structure, preventing transmitting signal from reducing a signal deciding performance, increasing the number of code multiplex and enhancing transmission efficiency.
According to a first aspect of the present invention, there is provided a code-multiplexing communication apparatus including: a splitting unit for splitting incoming serial transmitted data into N number of signal sequences; N number of spread units for performing out a spreading for each of the N number of signal sequences with use of a spread code; an adding unit adding the N number of signal sequences with the spreading processed by the N number of spread units to output code-multiplexed signal; and a modulating unit for modulating the code-multiplexed signal, in which a filter unit is also provided that it has an inverse characteristic to a frequency characteristic of an autocorrelated distortion caused by the spreading.
The filter unit may be provided on succeeding stages of either the N number of spread units or the adding unit.
The filter unit may include a transversal type filter having a plurality of delay elements, a plurality of multipliers, and a plurality of adders. It may also be a filter having the plurality of delay elements and a read-only memory.
According to a second aspect of the present invention, there is provided a code-multiplexing communication apparatus including that incoming serial transmitted data is split into N number of signal sequences, a spread spectrum is performed for each of the signal sequences with use of spread code, the N number of signal sequences with the spreading processed is then added each other, and a code-multiplexed signal modulated and transmitted is received, in which the code-multiplexing communication apparatus also includes a correlating unit for performing a de-spreading for incoming a received signal, and a filter unit is provided on a preceding stage of the correlating unit, the filter unit having an inverse characteristic to a frequency characteristic of an autocorrelated distortion caused by the spreading.
The filter unit may also include either a transversal type filter having a plurality of multipliers and a plurality of adders or a filter having a plurality of delay elements and a read-only memory.
According to a third aspect of the present invention, there is provided a code-multiplexing communication apparatus for transmitting code-multiplexed data with use of a spread spectrum, comprising: a spread code generator generating a spread code for performing the spreading, for outputting phase displaced signals each split into number of N; a splitter converting incoming serial transmitted data into N number of signal sequences, for transmitting the signal trains in parallel; N number of spreaders for performing the spreading for the N number of signal sequences with use of the spread code; N number of filters for filtering output signals from the N number of spreaders with use of an inverse characteristic to a frequency characteristic of an autocorrelated distortion caused by the spreading; an adder for adding outputs of the N number of filters; a transmitter having a modulator for modulating an output signal from the adder to output a transmitting signal; a de-spread code generator for generating a spread code for a de-spreading and outputting the spread code; a correlator performing a correlated calculation of an incoming received signal and the spread code to perform the de-spreading; an equalizer for removing a transmission path distortion from output signal of the correlator; and a receiver having a coupler for assembling receiving data by performing an inverse operation for an output signal from the equalizer to an operation performed by the splitter.
According to a forth aspect of the present invention, there is provided a code-multiplexing communication apparatus for transmitting code-multiplexed data with use of a spread spectrum, comprising: a spread code generator generating a spread code for performing the spreading, for outputting phase displaced signals each split into number of N; a splitter converting incoming serial transmitted data inputted into N number of signal sequences, for transmitting the signal sequences in parallel; N number of spreaders for performing the spreading for the N number of signal sequences with use of the spread code; an adder for adding outputs of the N number of spreaders; a transmitter having a modulator for modulating an output signal from the adder to output a transmitting signal; a filter for filtering an incoming received signal with use of an inverse characteristic to a frequency characteristic of an autocorrelated distortion caused by the spreading; a de-spread code generator for generating a spread code for a de-spreading and outputting the spread code; a correlator performing a correlated calculation of an output signal from the filter and the spread code to perform the de-spreading; an equalizer for removing a transmission path distortion from output signal of the correlator; and a receiver having a coupler for assembling receiving data by performing an inverse operation for an output signal from the equalizer to an operation performed by the splitter.
According to a fifth aspect of the present invention, there is provided a code-multiplexing communication apparatus for transmitting code-multiplexed data with use of a spread spectrum, comprising: a spread code generator generating a spread code for performing the spreading, for outputting phase displaced signals each split into number of N; a splitter converting incoming serial transmitting data into N number of signal sequences, for transmitting the signal sequences in parallel; N number of spreaders for performing the spreading for the N number of signal sequences with use of the spread code; an adder for adding outputs of the N number of spreaders; a filter for filtering an output signal of the adder with use of an inverse characteristic to a frequency characteristic of an autocorrelated distortion caused by the spreading; a transmitter having a modulator for modulating an output from the filter to output a transmitting signal; a de-spread code generator for generating a spread code for a de-spreading and outputting the spread code; a correlator performing a correlated calculation of an incoming received signal and the spread code to perform the de-spreading; an equalizer for removing a transmission path distortion from output signal of the correlator; and a receiver having a coupler for assembling receiving data by performing an inverse operation for an output signal from the equalizer to an operation performed by the splitter.
As aspects described above, the code-multiplexing communication apparatus has a filter on either the transmission side or reception side for previously removing the autocorrelated distortion caused by the spreading. According to such constitution, the affection of autocorrelated distortion does not emerge on the transmission characteristic when a communication performs under strict condition of subjecting to the autocorrelated distortion which affects the transmission characteristic and also when a numerous data transmission performs with increase of the number of code multiplex, enabling the numerous data and high quality transmission even under inferior condition of transmission path characteristic.
Furthermore, the autocorrelated distortion is previously removed prior to performing the correlated calculation for the de-spreading, increasing the number of code multiplex, sufficiently removing the transmission path distortion by the equalizer, and enabling high reliable data transmission.
The filter for removing the autocorrelated distortion can be incorporated in a desirable portion of the circuit in consideration of the number of code multiplex and the size of circuit as a whole, allowing the latitude of design.